Monitoring every minute of
every day

That's why the District's Monitoring Division
technicians, chemists, and meteorologists continuously
maintain and operate the sophisticated gaseous pollutant
analyzers, particle collectors, and weather sensors at
monitoring stations in Ventura, Piru, Simi Valley, Thousand
Oaks, El Rio, and Ojai to determine the type and level of
pollutants in the outside air. These monitoring stations
also measure relative humidity, ultraviolet and solar
radiation, barometric pressure, visibility, surface
temperature, winds, and precipitation. Click
here to
obtain site information for each monitoring station in
Ventura County. You will also be able to view real-time
ozone and fine particulate levels recorded at each station.

Because weather conditions are crucial to the formation
and movement of air pollution, each monitoring station also
measures atmospheric conditions. A seventh monitoring
station, called an "atmospheric profiler", measures, in
three dimensions, temperatures, wind direction, and wind
speed up to 6,000 feet above the surface.

Our quality assurance program ensures valid and
representative air pollution and weather data from each
monitoring station. Ventura County’s historical summaries of
pollutant data and air quality trends can be obtained by
clicking here.
Additional air quality data analysis is available from the
District upon request. Air quality data for the entire state
can be found at the California Air Resources Board’s Air
Quality Data
website.

You can access daily air quality, weather, and
agricultural burning reports and forecasts on this website
under Air Quality Forecast. Local newspapers also publish daily air
quality forecasts using the "Air Quality Index" (AQI). More
information about the AQI is available on this website under
Air Quality/Air Quality Index. Air quality conditions are
listed as "Good", "Moderate", "Unhealthy for Sensitive
Groups", "Unhealthy" (for all), and "Very Unhealthy". In
recent years, Ventura County's worst air quality days have
been in the "Unhealthy" range. Local air quality has
continued to improve, and the number of days in the
unhealthy ranges has been declining.

When air quality exceeds or is forecast to exceed the air
quality standards, the elderly, the very young, or those
with certain health problems should curtail their physical
activity, especially during the afternoon hours.

Smog

"Smog" is measured as ground-level ozone concentration.
To measure ozone concentrations in the air we breathe,
outside air is sucked through long, candy-cane shaped glass
tubes, where it moves to the ozone analyzer instrument
inside each monitoring station. Inside the instrument, the
air sample passes through a tube, where an ultraviolet (UV)
light is shined on the air sample. The amount of UV light
that passes through the air sample in the tube generates a
voltage signal that is proportional to the ozone
concentration in the specific air sample.

Carbon monoxide, sulfur dioxide, and oxides of nitrogen
are also analyzed using complex methods and continuous
analyzers.

Particles

Adverse health effects also occur due to
microscopic-sized particles in the air we breathe. These are
called "particulate matter" (PM). PM is monitored
differently than the gaseous pollutants - it is collected on
filters and weighed.

Air flows through the PM sampler like a vacuum. Very
small particles pass through the intricate tubing and onto
uncontaminated, pre-weighed filters. Afterwards, filters are
weighed again in the District lab. The amount of PM
pollution is determined by the weight of the PM collected on
the filter and the volume of air that flowed through the
sampler during PM collection.

The District monitors PM at regularly scheduled 24-hour
periods. PM is sampled on separate instruments for 2.5
micron and 10 micron sizes. (Ten microns equals about
one-seventh the diameter of a human hair).

Individual PM particles are too small to be seen, but
collectively they are visible - sometimes in the "haze", in
tailpipe smoke, or in windblown dust.

Because certain chemicals contained in PM samples can
have health effects of their own, or can contribute to the
formation of ozone through atmospheric interaction, some PM
samples from certain District monitoring stations are also
analyzed at outside laboratories for chemical content.

Learn more

Just because you can't see air pollution doesn't mean it
isn't there. That's why the District keeps a close watch on
air quality levels day in and day out - to protect public
health and welfare from the adverse effects of air
pollution. Rain or shine, the District's Monitoring Division monitors the air we breathe
throughout Ventura County's great outdoors.

For more information about monitoring the air or to
arrange a tour of the VCAPCD's lab or forecasting center,
call (805) 662-6959; or
write an e-mail to
Mallory Ham.